In recent years rapid innovations and developments have occurred with electronic products. With the continuous advance of semiconductor manufacturing technologies, electronic products have become more powerful and their prices have dropped. They are now widely accepted by the general public. Nowadays there are a wide variety of electronic products on the market. For the driving motor bearings used in information storage devices, there are oil impregnated bearings, ball bearings, and the like. The oil impregnated bearing has a lower price and thus cost advantage. However, its service life is shorter. The ball bearing has a longer service life, but it is more expensive and has a lower capability to withstand impact. These two types of bearings have their spindles in contact with the inner walls of the bearings. As a result, the motor tends to generate vibration and noise, and its service life becomes lower. On the other hand, dynamic bearings also are frequently used in the industry. The dynamic bearing is more precise and has a longer service life. It has become the mainstream in the market. However, it has starting friction and wearing problem that has yet to be overcome. Moreover, its production cost is higher, and production yield still does not reach the level desired. These issues remain to be resolved.
It is well known that the magnets of the same polarity repel each other. This property can be used to reduce the wearing when the spindle rotates. Thus it gradually becomes an important research and development direction in the industry. Some techniques are known in the art. For instance, U.S. Pat. Nos. 5,521,448 and 6,448,679 and so on disclose a technique regarding spindle motor having magnetic bearing. U.S. Pat. No. 5,521,448 discloses a technique regarding damping for passive magnetic bearings. It includes a passive magnetic bearing where the magnets are arranged radially in concentric rings. The rotating portion of the bearing is fixed to the shaft while the non-rotating stack is mounted to a fixed structure through a resilient material so that vibratory loads are carried in shear. Two sheets may be used, one on each side of the stationary bearing mount, so that the resilient material can be preloaded axially. The shear stiffness of the resilient material is adjusted so that it is low enough to permit the mount material to be strained enough to absorb a significant amount of energy and thereby produce system damping.
U.S. Pat. No. 6,448,679 discloses a type of passive magnetic support and damping system. It is comprised of a series of disks or annular rings of permanently magnetized material fixedly attached to the rotor of the machine. The stator portion is also comprised of a series of annular rings of permanently magnetized material, which are positioned concentrically with the rotor magnets. The stator and rotor magnets are formed and positioned such that a radial gap is present between said stator magnets and said rotor magnets. At least one, and preferably an even number, of the stator magnets are mounted in a damping material, which, in turn, is fixedly attached to the machine stator. This damping material may be an elastomeric material in response to shear or compressive strains. The soft mounted stator magnets provide damping to the system. The remaining stator magnets are fixedly attached to the machine stator and provide stiffness. By varying the number, size, and magnetic strength of the stator magnets mounted in these two ways, the stiffness and damping of the bearing assembly can be varied substantially independently.
However, the foregoing conventional techniques suit to large scale mechanism. In other words, it is so complex so that difficult to assemble, and unable apply to the small scale motor which are widely used in various types of electronic products, especially on data storage devices.
Besides, U.S. Pat. Nos. 6,050,785 and 6,097,120 disclose another type of damping system applied to a ball bearing or a sleeve bearing. They have a balance plate mounted above the circuit board corresponding to the magnet of the rotor, for providing a balancing force to ensure the rotor keeping at the center position corresponding to the stator. However, above-mentioned conventional techniques remain unstable. That is to say, the motors such as the ball bearing or the sleeve bearing are difficult to prevent from the rotor touching with the stator even with the balancing force between the balance plate and the magnet of the rotor. Moreover, the efficiency of the dissipation the vibration energy is limited because of lack of damper.
In short, there are still a lot of problems in the conventional techniques remained to be overcome.